EP0738656A1 - Retract control device of a movable structure - Google Patents

Abstract

The control mechanism has a transmission device (16) with disconnectable couplings (28) and springs (40). The springs act constantly against a mobile structure to move it into the retracted position once the coupling is disconnected. It incorporates an element (72) with a shape memory effect which can disconnect the coupling when it changes state as a result of a rise in temperature provided by an adjacent heater (76). The transmission device has a first component (24) which can be actuated by a control unit (14) in the form of an electric motor. It also has a second component (26) carrying the mobile structure. The coupling has a rod (46) which passes through the two components, joining them together by friction.

Description

Technical area

The invention relates to a device for controlling the retraction of a mobile structure normally connected to displacement control means by a transmission mechanism, in particular during a failure of these displacement control means.

A preferred application of such a device relates to the space domain. Thus, the optical systems on board spacecraft such as satellites and probes may no longer be able to fulfill their mission satisfactorily if an initially mobile structure used, for example to allow adjustment or calibration of the system, becomes locks in any position, in particular following a failure of the engine which normally controls its displacement, or a rupture or seizure of a mechanical connecting element.

State of the art

In document WO-A-91 19 645, a device for retracting a mobile structure has been proposed, in which this structure is brought back into a retracted position by spiral or torsion springs, when a pyrotechnic shear is actuated to disconnect the motor from the mobile structure whose movement is controlled by this motor.

In practice, such a pyrotechnic shear has a large size and mass. In addition, its implementation produces a shock which can damage certain elements of the optical system located nearby, or modify the setting.

Document WO-A-91 19 645 also proposes, as a variant, to replace the pyrotechnic shears with an electromagnetic suction cup or a thermal knife. However, these are again bulky and heavy systems. In addition, their reliability appears questionable.

Furthermore, as illustrated in document FR-A-2 648 199, it has already been proposed to embark on a spacecraft a member made of a shape memory material, to control the discharging of an element such as an antenna or solar panel, after launch.

In the same spirit, the document FR-A-2 667 842 also proposes, on a spacecraft, to use bodies made of shape memory material to control the unloading of rotary mechanisms comprising ball bearings, after the launch of the craft.

In these last two documents, the bodies made of shape memory material are always used to ensure discharge, that is to say the putting into working order of a system which must be clamped during launching in order to avoid it is not damaged by the violent vibrations which occur during this period. However, it is never envisaged to use such a member to control the retraction of a normally mobile structure.

Statement of the invention

The subject of the invention is precisely an original device making it possible to control, if necessary, the retraction of a mobile structure without inducing shock and in a particularly simple and reliable manner, for less bulk and mass than those of existing comparable devices.

According to the invention, this result is obtained by means of a device for controlling the retraction of a mobile structure, normally connected to displacement control means by a transmission mechanism, this device comprising disconnectable connection means. included in the transmission mechanism, and elastic means acting permanently on the mobile structure, to automatically bring the latter into a retracted position, when the disconnectable connecting means are disconnected, the device being characterized in that it further comprises a member made of a shape memory material, capable of acting on the disconnectable connecting means, in order to control the disconnection, when the state of the material changes, and heating means associated with said member, for command the change of state when crossing a predetermined temperature threshold.

In a preferred embodiment, the transmission mechanism comprises a first part capable of being actuated by the displacement control means and a second part carrying the mobile structure. The disconnectable connecting means then comprise a tie rod which crosses the first part and the second part, so as to normally join them together from one another by friction.

The tie rod then advantageously defines an axis of pivoting of the second part relative to the first part, the elastic means permanently exerting a pivoting torque between the first part and the second part, around this axis.

According to the preferred embodiment of the invention, one of the first and second parts comprises a tubular part which has two frustoconical end surfaces, the other of the first and second parts comprising two end pieces, one connected to the 'other by the tie rod, through the tubular part. Tapered bearing surfaces formed on the end pieces and complementary to the tapered end surfaces of the tubular part are normally pressed against these latter surfaces by the tie rod.

In this case, the member made of a shape memory material is a tubular member, mounted on the tie rod inside the tubular part, so as to be able to spread the frustoconical bearing surfaces formed on the end caps of the surfaces d 'frustoconical end formed on the tubular part, during the change of state of the material.

Advantageously, thermally insulating washers are interposed between the end pieces and the member made of a shape memory material, so as to ensure a uniform temperature rise of this member with a minimum of dispersion.

In the aforementioned embodiment, the frustoconical end surfaces and the complementary frustoconical bearing surfaces are not self-locking.

Preferably, the first part is pivotally supported by a fixed structure, around the axis defined by the tie rod. The displacement control means then comprise a motor supported by the fixed structure, and an output shaft of which drives the first part in rotation.

In the preferred embodiment of the invention, the tie comprises a region of least resistance, allowing its elongation under the action of the member made of a shape memory material, when the state of this material changes.

Brief description of the drawings

• la figure 1 est une vue de face, en coupe partielle, représentant un mécanisme permettant de commander le déplacement d'une structure mobile telle qu'un miroir, ce mécanisme incorporant un dispositif de commande d'escamotage conforme à l'invention ; et
• la figure 2 est une vue de côté du mécanisme illustré sur la figure 1.

A preferred embodiment of the invention will now be described, by way of nonlimiting example, with reference to the appended drawings, in which:

• Figure 1 is a front view, in partial section, showing a mechanism for controlling the movement of a movable structure such as a mirror, this mechanism incorporating a retraction control device according to the invention; and
• FIG. 2 is a side view of the mechanism illustrated in FIG. 1.

Detailed description of an embodiment

The mechanism illustrated in Figures 1 and 2 is intended to be carried on a spacecraft such as a satellite or a probe. This mechanism is designed to control the controlled pivoting of a mobile structure constituted by a mirror 10 (Figure 2), around a pivot axis XX. As illustrated schematically in broken lines in Figure 2, this pivoting allows, after launch, to bring the mirror 10 on the optical path 12 of an optical system (not shown), in a possibly adjustable position. In this position, the mirror 10 makes it possible to perform an operation on the optical system such as a calibration or an adjustment. When this operation is completed, the operation of the optical system supposes the erasure of the mirror 10 in its position shown in solid lines. If, for any reason, this deletion cannot be obtained, the optical system becomes inoperative.

The mechanism shown in FIGS. 1 and 2 comprises a stepping electric motor 14 constituting means for controlling movement of the mirror 10, as well as a transmission mechanism 16, through which the electric motor 14 drives the mirror 10. L the assembly is mounted on a fixed support structure 18 intended to be fixed on the structure 20 of the satellite or of the probe as shown in FIG. 2.

The body of the electric motor 14 is mounted directly in the fixed support structure 18. The latter also defines the pivot axis XX of the mirror 10, as will be seen later.

The transmission mechanism 16 comprises a pinion 22 wedged on the output shaft of the electric motor 14, as well as a first part 24 and a second part 26, normally joined to one another by disconnectable connecting means 28 .

The first part 24 of the transmission mechanism 16 comprises a tubular part 30 mounted in a bore 31 passing through the fixed support structure 18 along the axis XX. More precisely, the tubular part 30 is mounted in the bore 31 by bearings 32, such as angular contact ball bearings, so that the first part 24 can pivot freely around the axis XX relative to the structure fixed support 18. At one of its ends, the tubular part 30 of the first part 24 comprises a plate 34 terminated by a toothed sector 36 in engagement with the pinion 22. Thanks to this arrangement, it is understood that a rotation in either direction of the pinion 22, controlled by the electric motor 14, has the effect of rotating the first part 24 about the axis XX.

The second part 26 of the transmission mechanism 16 comprises a part 42 for carrying the mirror, as well as two parallel plates 38 which project towards the axis XX from the part carrying the mirror. The ends of the plates 38 are normally joined to the first part 24 by the disconnectable connection means 28. In order to ensure proper operation of these disconnectable connection means 28, the plates 38 have a certain suppleness or flexibility parallel to the axis XX. This result can be easily obtained by giving them a small thickness and by making them in an appropriate material.

The disconnectable connection means 28 belong to a device for retracting the mobile structure 10. When this retracting control device is actuated, the disconnectable connection means 28 disconnect the second part 26 from the first part 24. A spiral or torsion spring 40, the ends of which are fixed respectively to the first part 24 and to the second part 26, then automatically controls the pivoting of this second part in the anticlockwise direction by considering FIG. 2, until the mirror-carrying part 42 of the second part 26, which carries the mirror 10, comes to bear against a stop 44 formed for this purpose on the fixed support structure 18. The mirror 10 is thus automatically brought into the retracted position illustrated in solid lines in FIG. 2, whatever the position initially occupied by this mirror. In this retracted position, the mirror 10 is completely offset from the optical path 12, so so that the corresponding optical system can continue to be used without damage.

The retraction control device according to the invention will now be described in more detail, referring again to FIG. 1.

The disconnectable connecting means 28 comprise a tie rod 46 disposed along the axis XX and connecting the ends of the plates 38 through the tubular part 30, placed between these ends.

More specifically, a threaded end of the tie rod 46 is screwed into a removable end piece 48 forming the end of one of the plates 38. The end piece 48 is attached to this plate 38 by screws 50. The end of the other plate 38, terminated by a second end piece 52, is crossed by the tie rod 46. In its part which projects beyond the second end piece 52, the tie rod 46 also comprises a threaded part on which a nut 54 is received. Beyond of its threaded part receiving the nut 54, the tie rod 46 comprises an operating head 56 which makes it possible to screw the tie rod 46 into the removable end piece 48, by means of a key. On their opposite faces, the end pieces 48 and 52 respectively have frustoconical bearing surfaces 58, 60.

The tie rod 46 is mounted coaxially inside the tubular part 30 of the first part 24, so that the frustoconical bearing surfaces 58 and 60 formed on the end pieces 48 and 52 are normally pressed against surfaces of frustoconical ends 62 and 64, complementary to surfaces 58 and 60 and formed in this tubular part 30.

More specifically, the frustoconical end surface 62 is formed directly on the tubular part 30 at its end carrying the plate 34, while the frustoconical end surface 64 is formed on a ring 66 which slides freely on the opposite end of the tubular part 30. This arrangement in two parts makes it possible to ensure effective wedging of the inner rings of the ball bearings 32, by means of a spacer 67 placed between these rings, when a compressive force is exerted between the ends 48 and 52 by the tie rod 46.

Opposite the frustoconical bearing surface 58, the attached endpiece 48 supports a baluster 68 terminated by a disc 70. The baluster 68 is arranged along the axis XX, inside the spiral or torsion spring 40 In practice, the end of this spiral or torsion spring linked to the second part 26 is fixed to the disc 70 as shown in FIG. 1.

In addition to the disconnectable connecting means 28 and the elastic means constituted by the spiral or torsion spring 40, the mirror retraction control device 10 comprises a tubular member 72, made of a shape memory material, placed between the end pieces. 48 and 52 around the tie rod 46 and inside the tubular part 30 of the first part 24. The member 72 made of a shape memory material is dimensioned in such a way that its length does not prevent it from joining by friction parts 24 and 26, via the frustoconical surfaces 58 and 62 on the one hand and 60 and 64 on the other hand, when the nut 54 is tightened and when the mechanism is at a normal operating temperature.

On the other hand, when the temperature of the member 72 made of a shape memory material rises above a predetermined temperature threshold (comprised, for example, between 60 ° C. and 100 ° C.), the dimensioning is such that the elongation of this member (for example, about 1 mm) has the effect of spreading the end pieces 48 and 52 enough to eliminate the connection by friction of the parts 24 and 26. For the separation of these parts to be carried out correctly, it should be noted that the friction connections normally provided between the frustoconical complementary surfaces 58 and 62 on the one hand and 60 and 64 on the other hand are not self-locking.

So that the elongation of the member 72 in a shape memory material does indeed have a spacing of the end pieces 48 and 52, it can be seen in FIG. 1 that the tie rod 46 has a region 74 of less resistance. This region 74 may in particular be constituted by an area in which the diameter of the tie rod 46 is sufficiently reduced to allow its elongation, when a force tending to spread the end pieces 48 and 52 is applied by the member 72 in a memory material of form.

In order to ensure that the material constituting the tubular member 72 crosses its phase change temperature, this tubular member is surrounded by heating means 76 constituted for example by an electrical resistance. The electrical supply of the resistor constituting the heating means 76 is provided from an external source (not shown) by electrical conductors which do not appear in the figures.

In the embodiment shown, an insulating washer 78 is placed at each end of the tubular member 72 in a shape memory material, in order to ensure a homogeneous rise in temperature and with a minimum of dispersion. In addition, a washer of thickness 80 and a support spacer 82 are interposed between the end piece 52 and the insulating washer 78 adjacent. Furthermore, a support ring 84 is interposed between the end piece 48 and the adjacent insulating washer 78.

The support spacer 82 and the support ring 84 allow the elongation of the tubular member 72 to be transmitted to the end pieces 52 and 48. The thickness washer 80 is machined on demand in order to ensure the minimum clearance correct operation of the tubular member 72 in a shape memory material.

When launched, the mechanism shown in the figures is locked in the retracted position shown in solid lines in Figure 2 by a stacking device (not shown) associated with the stop 44. This stacking device can be produced in any manner and is not part of the invention.

When the satellite or the probe is in operational conditions, the stacking device is actuated so as to release the mechanism. The mirror 10 can then be brought as desired to the desired position, using the electric motor 14 for example to carry out a calibration or an adjustment of the optical system. To allow the use of the optical system, it is then necessary to retract the mirror 10 by acting again on the motor 14.

Following an incident, due for example to a failure of the engine 14 or of its control system, it may become impossible to retract the mirror 10 using the engine 14. Under these conditions, the pursuit of the mission requires bringing this mirror into its retracting position shown in solid lines in Figure 2 by other means.

According to the invention, this retraction can be easily controlled by heating the tubular member 72 of a shape memory material up to the phase change temperature of this material, for example between 60 ° C and 100 ° C . This heating is provided by the heating means 76. When the phase change occurs, the tubular member 72 lengthens by a value (for example about 1 mm) sufficient to ensure detachment of the frustoconical surfaces 58 and 62 on the one hand, 60 and 64 on the other hand, by elongation of the region 74 of the tie rod 46. As soon as the detachment has taken place, the spiral or torsion spring 40, which acts permanently between the parts 24 and 26 to exert a pivoting torque between these parts, rotates the second part 26 anticlockwise when considering FIG. 2. The pivoting of the second part 26 continues until the part 42 mirror holder comes to bear against the stop 44 as is described previously.

The desired result is thus obtained without shock and by means of a particularly simple, light and space-saving retraction control device.

It should be noted that the invention is not limited to the embodiment which has just been described with reference to the figures. Thus, even if it is of obvious interest in the space field, it can also be used in other fields. Furthermore, the device can be used to control the retraction of any movable member, the mirror described is only one example in the particular case of an optical system. Finally, it should be noted that the movement of the movable member can be any movement such as rotation, translation, or a more complex movement.

Claims (10)

Device for retracting a movable structure (10), normally connected to displacement control means (14) by a transmission mechanism (16), this device comprising disconnectable connecting means (28) included in the transmission mechanism, and elastic means (40) acting permanently on the mobile structure (10), to automatically bring the latter into a retracted position, upon disconnection of the disconnectable connecting means (28), the device being characterized by the fact that it further comprises a member (72) of a shape memory material, capable of acting on the disconnectable connecting means (28), to control disconnection, during a change of state of the material, and heating means (76) associated with said member, for controlling the change of state when crossing a predetermined temperature threshold. Device according to claim 1, characterized in that, the transmission mechanism (16) comprising a first part (24) capable of being actuated by the displacement control means (14) and a second part (26) carrying the structure mobile (10), the disconnectable connecting means (12) comprise a tie rod (46) passing through the first part and the second part, so as to join them normally to one another by friction. Device according to claim 2, characterized in that the tie rod (46) defines an axis of pivoting of the second part (26) relative to the first part (24), the elastic means (40) permanently exerting a torque pivoting between the first part and the second part, around this axis. Device according to any one of Claims 2 and 3, characterized in that one (24) of the first and second parts comprises a tubular part (30) which has two frustoconical end surfaces (62,64), l 'other (26) of the first and second parts comprising two end pieces (48,52), connected to each other by said tie rod (46), through the tubular part, so that bearing surfaces frustoconical (58,60) formed on the end pieces and complementary to the frustoconical end surfaces formed on the tubular part are normally pressed against the latter surfaces by the tie rod. Device according to claim 4, characterized in that the member (72) made of a shape memory material is a tubular member, mounted on the tie rod (46) inside the tubular part (30), so being able to separate the frustoconical bearing surfaces (58,60) formed on the end pieces (48,52) from the frustoconical end surfaces (62,64) formed on the tubular part (30), during the change of state of the material. Device according to claim 5, characterized in that thermally insulating washers (78) are interposed between the end pieces (48,52) and the member (72) made of a shape memory material. Device according to either of Claims 5 and 6, characterized in that the heating means (76) are placed around the member (72) in a shape memory material. Device according to any one of Claims 4 to 7, characterized in that the frustoconical end surfaces (62,64) and the frustoconical bearing surfaces (58,60) are not self-locking. Device according to any one of Claims 3 to 8, characterized in that the first part (24) is pivotally supported by a fixed structure (18), around the axis defined by the tie rod, the control means movement comprising a motor (14) supported by the fixed structure, and an output shaft of which drives the first part in rotation. Device according to any one of claims 2 to 8, characterized in that the tie rod (46) comprises a region (74) of less resistance, allowing its elongation under the action of the member (72) made of a material to shape memory, when the state of this material changes.

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